1. Technical Field
The present invention relates in general to a disk drive unit and, in particular, to a system and method for controlling a hard disk drive and disk drive unit.
2. Description of the Related Art
A hard disk drive (hereinafter, a HDD), which is most commonly used as data storage means for computers, comprises a single or multiple magnetic disks on the same shaft, which is or are rotated by a spindle motor. Data reading and writing is performed by a magnetic head that is placed facing the magnetic disk, wherein the magnetic head is driven by an actuator, which is typically a voice coil motor (hereinafter, a VCM). The magnetic disk, magnetic head and actuator are accommodated in a chassis called disk enclosure. The disk enclosure is composed of a thin box-shaped aluminum alloy base and a top cover for sealing an opening of the base.
Some of the magnetic heads for data reading and writing comprise discretely a transducer for data writing and magnetization means for data reading. As magnetization means for data reading, what utilizes magnetoresistive (MR) effects or giant magnetoresistive (GMR) effects has been developed. The magnetization means for data reading that employs MR or GMR effects allows increasing the recording density since it is difficult to be affected by the noise.
A magnetic head is supported in place on a member called slider. Accordingly, a term “slider” may refer to what includes the magnetic head or sometimes refers to a magnetic head itself. Namely, a magnetic head and slider are sometimes recognized as equivalents. When the magnetic head reads data from or writes data to the magnetic disk, the magnetic head (i.e., slider) flies over the surface of the disk at a predetermined amount. This flying of the magnetic head over the magnetic disk is caused by an air bearing induced above the magnetic disk by the rotation of the disk. In connection with this, the surface of the slider facing the magnetic disk is called air bearing surface (hereinafter, an ABS), whose aspects has a great influence on the flying of the slider.
The flying height of the slider over the magnetic disk is preferably small when giving greater importance to data reading and writing. This is because magnetic interactions between the magnetic disk and the magnetic head can be thoroughly ensured. Therefore, it is desirable for high-density magnetic recording that a slider with a low flying height is employed.
3. Problems to be Solved by the Invention
When performing data reading and writing using a slider with a low flying height, write failures called jamming write have been observed as shown in FIG. 10. It turned out that this phenomenon particularly occurs when the magnetic head has been engaged in the track following operation near a certain cylinder for a long time. It is therefore an object of the present invention to reduce write failures.